M (Maria) Scheel

Can Arctic Soil microbes impact carbon lost from their warming system?

In my Villum International Postdoc Project CREEPIES, I am investigating exactly that question. While soils are the biggest terrestrial carbon (C) reservoir, which is at risk of irreversible erosion (IPCC, 2021). Especially the vast Arctic permafrost, which remains frozen throughout the year, contains over half of all global soil C, equal to twice the current global atmospheric C (Tarnocai et al., 2009, Hugelius et al., 2014). As the Arctic warms at least four times faster than the global rate (IPCC, 2021), these permafrost C pools become available for microbial degradation them into carbon dioxide (CO2) and methane (CH4) (Turetsky et al., 2020). Predicting the magnitude of C release still proves difficult though, because on top of environmental parameters it is also biologically controlled through a complex soil food web (Ernakovich et al., 2022), such as microbial predation in soils (feeding on bacteria by microeukaryotes, such as single-cell protists and larger nematodes; Rønn et al., 2012, Thakur & Geisen, 2019). Although studies in temperate regions showed that through microbial predator impact on the microbial community composition and activity, increased the C, nitrogen and phosphorous cycling (Geisen et al., 2018), despite their abundance in permafrost (Scheel et al., 2023), their ecological function and importance for C-cycling in permafrost remains unknown. We further don’t know yet if protists in thawing permafrost soils preferably prey on specific taxa, such as CH4-releasing (methanogenic) Archaea or CH4-consuming (methanotrophic) microbes, and hence their potential impact on CH4 emissions.

In my proposed two-year international postdoctoral stay at Wageningen University I aim to identify protists in Arctic soils and quantify their predation-related impacts on the microbial community composition and consequently resulting changes in C sequestration during artificial permafrost thaw.

Upon successfully conducting the three work packages, I will be able to improve calculation in predictive models about permafrost C loss, based on the relative impact soil moisture and temperature have both on C mineralising microorganisms as well as their predators. These findings could bear the potential to be applied directly in order to finetune predictions on Arctic soils vulnerability and increase our knowledge about ecological cascades in response to global warming, and how species interactions impact the expected climate change driven C loss from eroding soils.

The project setting with the proposed research question if microbial predation inhibits or accelerates carbon loss from eroding soils. Image credit: Maria Scheel.